This invention relates to a positioning system, which measures a position of a node having a wireless transmission function, and particularly to a positioning system, a positioning method, and a positioning server, which are highly accurate in position detection.
As a conventional representative method of measuring a node position, there is a method of measuring the node position by use of a signal from a satellite such as a GPS.
As another conventional method of measuring the node position, there is a method, in which the node receives signals from a plurality of access points, and the node position is calculated from differences among received times of the signals.
Specifically, there has been proposed a method of detecting a position of a terminal station, which is used for a cellular phone system, and in which differences among received times of signals transmitted from access points to the terminal station (time differences T1−T2 and T3−T2 between propagations of the signals from the respective access points to the terminal station) are calculated, the time differences between the propagations are multiplied by the velocity of light, and distance differences between the propagations of the signals from the terminal station to the respective access points are calculated, the distance differences being represented as:D1−D2=c(T1−T2); andD3−D2=c(T3−T2)(for example, refer to JP 07-181242 A).
Moreover, there has been proposed a method of detecting a position of a node, which is used for a wireless LAN system, and in which time differences among receipts of a signal transmitted from the node (terminal station) by the access points (time differences Ti−T1 among the receipts by the respective access points) are calculated, the time differences among the receipts are multiplied by the velocity of light, and distance differences {|P−Pi|−|P−P1|}=c(Ti−T1), i=2, . . . , n among propagations of the signal from the node to the respective access points are calculated (for example, refer to “Integrated Wireless LAN Access System—Study on Location System”, Atsushi Ogino and 5 others, Proceeding of the 2003 IEICE Society Conference, The Institute of Electronics, Information and Communication Engineers, B-5-203, p. 662).